The following is a compilation of the procedures used by Scientific
Instrument Services for the cleaning of mass spectrometer sources over the last
25 years. This article incorporates
the current techniques used at SIS as well as procedures reported in our Mass
Spec Handbook of Service (published in 1983 and now out of print), articles
published in back issues of the "Mass Spec Source Newsletter" as well
as application notes published on the SIS web site (http://www.sisweb.com).
These methods have been tested and modified over the years with the
availability of new equipment and with the input from many other mass
spectrometer users. In addition we
have included several alternative techniques for the same operation, when these
methods have been recommended by the instrument manufacturers.
As a result this article provides for a comprehensive resource of
techniques and methods for the cleaning of mass spectrometer sources for most
mass spectrometers.

This article covers the general service and cleaning of the mass
spectrometer sources for a wide range of instrument models but may not be all
inclusive. Most, but not all, of
the metal parts in a mass spectrometer source can be cleaned by the following
techniques.

When cleaning a mass spectrometer source, there may be components that
cannot be cleaned or that must be handled carefully and without the use of any
abrasive cleaning tools. Items such
as alumina coated metal parts, gold plated parts, ceramic insulators, O Rings,
Vespel® insulators and other polymer components must be handled and cleaned by
techniques which will not damage these components.
Cleaning methods for these components are discussed at the end of this
article. In addition, the
specialized methods outlined in the instrument manufacturers' manual may have
notes on how to handle these components. Check
your instrument manufacturers' manuals for specific information on the cleaning
of the mass spectrometer source and take note of parts which require special
handling or alternative cleaning methods.

There is no regular schedule for cleaning the mass spectrometer source.
The source should be cleaned when the mass spectrometer symptoms indicate
that the source is contaminated. These
symptoms include poor sensitivity, loss of sensitivity at high masses, or high
multiplier gain during an auto tune.

The cleaning and service of the mass spectrometer source begins with the
removal of the source from the vacuum housing, followed by disassembly, cleaning
and polishing, washing and finally reassembly and testing.
The various steps are outlined below and this article follows this
general outline.

This operation begins with the shutdown and venting of the mass
spectrometer vacuum system. The
mass spectrometer vacuum chamber must be at atmospheric pressure before the
vacuum housing can be opened and the mass spec source removed.

CAUTION: All
power to the mass spectrometer must be turned off and all vacuum pumps must be
turned off. Allow the source to
cool before beginning source removal.

Depending on the manufacture and design of the mass spectrometer source
and mounting system, the removal of the mass spec source from the vacuum housing
can be easy or quite difficult. The
difficulty usually occurs due to plumbing and electrical wiring of the source.
For these difficult situations it is often advisable to check the
manufacturers' manual to make sure that there are detail directions, schematics
or photographs to demonstrate the removal process.
If these are not available, it is advisable to take photographs of the
source and mounting before you begin.

CAUTION: Take
care not to get fingerprints or other contamination on any of the source, source
mounting assembly or inside the vacuum chamber. Lint free nylon gloves should be
used for all disassembly and reassembly operations.

After the source has been removed from the mass spectrometer, it should
be placed on a clean lint free cloth for the source disassembly operations.

Disassembly of the MS Source

After the source has been removed from the mass spectrometer it must be
disassembled before cleaning is started. Again
check the manufacturers' manuals for detailed drawings or pictures of the source
assembly and disassembly. If this
information is not available, then you should take pictures of the source before
disassembly begins and at the various stages of disassembly.
At SIS we often are asked to clean a source that is quite complicated.
Before we begin we take digital photographs of the source from various
angles and take additional photographs during the disassembly process.
These color photographs have proved quite valuable when reassembling the
sources. In the photographs pay
particular attention to electrical wire hookups and the orientation of parts on
the source block. Also take note of the magnets and the orientation of the
magnet poles on the source block. During
the disassembly process, make notes on the photographs or drawings as needed.
These precautions will save a lot of time in the future.

CAUTION: Use
caution when removing thermocouples, heaters and other small delicate parts in
the mass spec source. These parts
are easily damaged during removal and may need to be replaced if damaged.

Normally disassembly begins with removing electrical wire leads and
connectors. Often the mass spec
source can be removed from its mount by just disconnecting the electrical leads
at the source itself. This is
preferable since the lead will not need to be completely removed and its
orientation and location will not be changed when the source is ready to
reassemble. At other times it is necessary to completely remove the
leads. If this is necessary, it is
important to note the location of each lead as well as its orientation so that
it can be put back in the same relative position when the source is reassembled.

CAUTION: Use
caution in the removal of small screws from the mass spectrometer source.
These screws can be easily broken off in the source body and not be
repairable. If screws are stuck or
frozen, do not force.

If the manufacturer has
disassembly instructions in the manual, they should be followed, otherwise parts
are normally removed in a logical sequence from the outside to the inside.
Use care in removing screws so as not to damage the screw head slots.
If a screw is tight or frozen in position, do not force it. In this case other techniques may help such as the use of
penetrating oil, putting the part with the frozen screw into an ultrasonic
cleaner or heating the parts to try to unstick the screw.
If a screw breaks off in the source block, it may not be repairable and a
new source block may need to be purchased.
The instrument shops at SIS have had some success in removing broken
screws for our customers - so you can try us if you have no other alternative.

As the parts are disassembled,
place the metal parts which will be abrasively cleaned in one beaker and the
other parts such as ceramics, insulators, plastic parts and other parts which
cannot be polished in a separate beaker.

II.
Cleaning Techniques for Metal Parts

The purpose of cleaning the mass spectrometer source is to remove
deposits and contamination that can interfere with the mass spectrometer
performance and prevent it from operating at optimum performance and
sensitivity. The amount and degree
of cleaning depends on the construction material of the source parts and their
degree of contamination.

Part Types

Cleaning Methods

Stainless Steel Parts

Abrasive
cleaning including buffing and abrasive cleaning followed
by solvent cleaning and low temperature bake out

Ceramic Insulators

Sandblasting,
Acid Washing, Solvent Cleaning, Bake out

Berilium Oxide Insulators

Solvent wash followed by low temperature bake out

Oxide coated metal parts

Solvent wash followed by low temperature bake out

Macor Ceramics

Solvent
wash followed by low temperature bake out

Vespel Insulators

Solvent wash followed by low temperature bake out

Gold Plated Parts

Solvent
wash followed by low temperature bake out

O Rings

Solvent wash followed by low temperature bake out

PRT & Thermocouples

Low Temperature bake out

A number of techniques are
available for the cleaning of the metal source parts. At SIS we have used a combination of polishing with motorized
power tools and hand polishing with Micro Mesh abrasive sheets. For parts that
may have stubborn deposits, we often use small sandblaster with glass beads
abrasives (but this is not normally needed).
Other abrasive sheets have also been used (such as those sold by Agilent),
but the Micro Mesh products are a finer grit and produce finer finishes on the
stainless steel parts.

Parts of the source that come in
contact with the sample or ion beam should be thoroughly cleaned as described
below. However surfaces that do not
come into direct contact with the sample (such as the source mounting brackets)
do no normally need to be cleaned to the same extent, unless the contamination
can contribute to the contamination of the source when it is reinstalled into
the mass spectrometer. Normally just rinsing in solvent and drying is all that
is required of these less critical components.

II. A. a. Cleaning with Motorized Buffing Tools

Tools Required

Supplies listed previously

Dremel Moto-Tool

Flt Buffing wheels

Polishing compound

Polishing and buffing stainless steel parts with a motorized buffing
wheel is a quick and effective method for cleaning the residues off the
stainless steel source parts and restoring the metal finish to a bright mirror
finish. In our labs we have used
the Dremel Moto-Tool, The Foredom Motor Tool and a small bench mounted buffing
wheel. The Dremel Moto-Tool is a
good choice for the laboratory because it can have many other applications in
the instrument laboratory. Parts
cleaned by the following techniques will be highly polished and will be free
from fine scratches, which collect contamination rapidly and necessitate
frequent cleaning. The
initial cleaning may involve much time and effort.
However the metal surfaces will stay cleaner longer (since the fine
scratches in the metal surface which collect contamination are absent) and
future cleaning will be much faster and easier.

The Dremel Moto-Tool is normally used with small felt buffing wheels
mounted on a small mandrel. Polishing
speed of 20,000 to 30,000 rpm are normally used for polishing parts. The buffing
wheels are available in a number of shapes including 1" diameter disks,
1/2" diameter disks and small pointed cylinders for getting into corners.
A fine metal finishing abrasive is used with the felt buffing wheel.
The Dremel polishing rouge is a good general buffing abrasive, but other
buffing abrasives are available from your local hardware store.
Apply the abrasive paste in a thin film on the felt buffing wheel.
Polish thoroughly to remove all carbon residues and scratches. When
buffing parts, take care not to force the part into the buffing disc.
Let the wheel and the abrasive do the work.
When the cleaning appears to slow down, add more abrasive to the sheel.
Polish the metal to a high luster. The
more you polish, the more of a mirror like finish you will obtain.

CAUTION - SLITS - Be careful not to round the edges
of slits and edges on the metal ion focusing plates on the mass spec source.
Buff in the direction of the slit so as not to round the edges.
On the edges of the slits buff lightly for minimal metal removal or
preferably use the Micro Mesh polishing board described below on these slit
edges.

II. A. b. Cleaning
with Abrasive Cloths

Tools Required

Supplies listed
previously

Micro Mesh abrasive
cloths

Micro Mesh polishing
board

The shops at SIS have been using Micro Mesh abrasive cloths and polishing
boards for many years to clean and polish the stainless steel source parts.
The Micro Mesh is a cushioned abrasive on which the abrasive crystals
float rather than remain in a fixed position on its backing.
As a result the surfaces of the materials being cleaned will have minimal
surface scratches from the abrasive as compared to other abrasive materials. The four finest grits (4000, 6000, 8000 and 12000) are
normally all that is required for mass spec source cleaning. Use the courser grits to remove the carbon residue from the
source and then use the next finest grit until you finish the source cleaning
with the 12000 grit Micro Mesh. Using
this product in this step like manner will produce a mirror like surface much
like buffing above. The abrasive sheets can be cut into smaller pieces or folded
to various shapes to fit the contour of the item being polished.

The Micro Mesh polishing boards are good for cleaning
slits. Hold the slit
perpendicular to the board while polishing.
This will clean the slit edge, without rounding the edges of the slits.

II. A. c. Cleaning
with Abrasive Powders

Tools Required

Supplies listed
previously

Aluminum Oxide abrasive
(600 mesh)

Cotton swabs

Some of the instrument manufacturers recommend cleaning the source using
an abrasive aluminum oxide powder. SIS
sells a 600 grit aluminum oxide abrasive for this purpose.
Use an abrasive slurry of the aluminum oxide abrasive with methanol or
water. Cotton swabs work quite well
with this abrasive slurry. These
small cotton swabs enable the cleaning of corners inside the mass spec source.
The only disadvantage of this product is that it is more abrasive than the
previous techniques and the finished surface will not have a high metal luster.
Courser abrasives are not recommended for cleaning mass spectrometer
sources.

II. A. d. Sandblasting

Tools Required

Supplies listed previously

Miniature Sandblasterwith exhaust system

Aluminum oxide abrasive,
400 grit

On occasion we have used miniature sandblasters to clean mass
spectrometer sources. Normally
glass beads abrasives are used at low pressures to remove stubborn residues from
metal parts. Sandblasting is not
normally used on the source stainless steel parts (and should never be used on
source slit edges). However
sandblasting works quite well in removing baked on carbon stains on metal
surfaces and is frequently used to clean the ceramic insulators from the mass
spec source. Several pieces of
equipment for this purpose are described in the SIS catalog.
(See the Miniblast Sandblaster and Air Eraser products in the SIS
catalog).

II. B. Washing Procedures

Tools Required

Supplies listed
previously

Variety of glass beakers

Ultrasonic Cleaner

Detergent (Alconox or Mr.
Clean)

Water or other solvents
as required

After the metal parts have been cleaned and polished by the above
procedures, they must be cleaned to remove all trace residues of the buffing
compounds and abrasive materials. Normally
solvents are used for this purpose. In
the past many manufacturers have recommended the use of chlorinated solvents and
toluene for this purpose. However
we do not think that these solvents are necessary.
The following procedure is used at SIS for washing instrument parts after
cleaning. Below are listed some the solvent rinsing sequences reported by
various manufacturers during the last 25 years

Industry recommended solvent
washing sequences

SIS

Agilent

Thermo-Finnigan

Dupont

Mild Detergent

Methylene
Chloride

Water

Water

Water

Acetone

Methanol

Isopropylalcohol

Acetone

Methanol

1,1,1-Trichloroethane

Toluene

Methanol

Ethyl
Ether

CAUTION: Many
of these solvents are hazardous. Protective
equipment including safety glasses and rubber gloves should be used with these
solvents and all operations must be conducted in a laboratory fume hood.

CAUTION: When
washing the metal parts in the ultrasonic cleaner, do not let metal parts come
in contact with each other. Part
vibrating against one another may cause scratches on the surfaces of the parts.
Do not leave parts in the ultrasonic cleaner for more than 5 minutes.
If the parts are not clean in less than 5 minutes, either clean solvents
or other solvents may be required.

First the parts are washed in an ultrasonic cleaner in water with a
detergent. We have used both
Alconox and the commercial cleaner Mr Clean for this purpose.
The purpose of the first cleaning with detergent is to remove the buffing
compound residues and other oil residues from the cleaning process.
A toothbrush with the detergent solution can be used initially to remove
the heaviest deposits of abrasive cleaning compounds.
The parts are put in the ultrasonic cleaner and sonicated for at least
two minutes. Repeat this
process with several new solutions of the detergent until the parts are clean. Then wash the parts several times in the ultrasonic cleaner
with clean water until no soap residues are present. Finally rinse the parts in Acetone to remove all water
residues and do a final rinse in Methanol.

II. C. Baking
and Drying

Tools Required

Supplies listed
previously

Laboratory Oven

Gloves or tweezers

After the parts have been washed they are normally baked out in a
laboratory oven at 100 to 150 degrees C for at least 15 minutes.
If properly cleaned the parts should have no residues of cleaning
materials and be spot fee. After
the parts are allowed to cool they should not be touched with the bare hand.
Use nylon or cotton gloves, lint free cloths and tweezers to handle all
clean parts.

CAUTION: When
parts are removed from the oven they are hot.
Do not touch the parts until cool. Do not touch the parts with nylon
gloves when hot or the nylon may melt onto the metal parts.

When the parts are finished they should be placed on a
clean lint free cloth and proceed with the assembly operations.

III.
Cleaning Ceramic Insulators

III. A. Abrasive
Cleaning

Tools Required

Supplies listed
previously

Miniature Sandblaster
with exhaust system

Aluminum oxide abrasive,
400 grit

The preferred method for cleaning alumina ceramic source insulators at
SIS, is to first sandblast the ceramics using 400 grit aluminum oxide abrasive
in a miniature sandblaster. This
technique will normally remove most carbon residues.
After sandblasting, the parts should be blown off thoroughly to remove
any abrasive residues and then rinsed in an Acetone bath.
It is not recommended that ceramic insulators be cleaned in an ultrasonic
cleaner since this may damage them. Finally
the ceramic insulators are baked out in an oven at a temperature of at least 150
degrees C. Because ceramics can
adsorb solvents more readily than metal parts, they should be baked out for at
least 30 minutes at 150 degrees C.

CAUTION: Be
certain that the ceramics you are cleaning are alumina ceramic. Do not sandblast
Berilium ceramics (these are considered toxic) and do not sandblast Macor or
other machinable ceramics because they are too soft and will be destroyed by the
sandblasting procedure.

When the parts are cool, they should be removed from the oven and placed
on a clean lint free cloth.

CAUTION: When
parts are removed from the oven they are hot.
Do not touch the parts until cool. Do not touch the parts with nylon
gloves when hot or the nylon may melt onto the metal parts.

III. B.
High Temperature Bake Out of Ceramics

Tools Required

Supplies listed
previously

Muffle Furnace

Miniature Torch

Another technique often used to clean ceramics is by baking them out in a
muffle furnace at a temperature where they just begin to glow (about 1000
degrees C) This will burn off any
carbon residue. We have also
cleaned ceramics by just heating with a miniature torch to accomplish the same
results, but be careful to heat and cool the ceramics slowly with this technique
so as not to produce a high thermal shock to the ceramics which will cause them
to crack.

Other manufacturers have recommended cleaning of ceramics using a
dichromate solution (which will turn the ceramics green in color) or by
immersing in Nitric acid or aqua regia. We
do not recommend either of these methods due to the hazards involved in handling
these chemicals.

CAUTION: If
acids are used in the cleaning of ceramics, all operations must be performed in
a laboratory fume hood with the use
of protective clothing, gloves and safety glasses. These operations should only be performed by individuals
trained in the safe and proper handling of these chemicals.

Cleaning Vespel parts, O Rings and other polymers

Tools Required

Supplies listed
previously

Glass laboratory beakers

Untrasonic Cleaner

Solvents - Methanol

Some of the parts in the mass spec source may include polymers and cannot
be cleaned by any of the above procedures.
Normally these parts are cleaned by immersing in Methanol in an
ultrasonic cleaner for several minutes. Following
this cleaning, the parts are put into an oven and baked out at 100 to 150
degrees C for at least 15 minutes. If
this does not clean the parts, they will probably need to be replaced.

V.
Reassembly

Tools Required

Supplies listed
previously

After all the parts are cleaned and baked out, the source should be
assembled in the reverse order that it was assembled.
Be sure to use nylon gloves and tweezers to handle all parts.
Do not touch them with your bare hands.
Assemble source on a clean lint free cloth. Assembly is always more
challenging than the disassembly operation.
It requires some dexterity and a good deal of patience to handle small
screws and the source parts using tweezers and the jewelers screwdrivers.
Use care to tighten all parts securely, but do not over tighten the
screws as you may damage the screw head slots or make it impossible to remove
these screws in the future.

VI.
Filament Installation and Alignment

Tools Required

Supplies listed
previously

The installation of the filaments and heaters is normally the last step
before the source is installed back into the mass spec vacuum system.
If the mass spec has a collector, it is often best to install the
filament before the collector. One
can then check the filament alignment by looking thought the ion exit hole where
the collector would normally be. This
is the optimum way to make sure the filament is perfectly aligned in the source.

VII.
Testing

Tools Required

Volt Ohm Meter

After the source as been completely reassembled and the electrical leads
installed. The components should be
checked for continuity and leaks. The
following components are normally checked with a volt-ohm meter using the
resistance scale.

After all testing is complete the source can be reinstalled into the MS
vacuum housing. After installation
the above readings can again be checked at the lead ends where they exit the
vacuum chamber. This will assure
that the leads are properly connected.